There it was. Right there in the center of the speedometer, telling me it was time to replace the front brake pads. Bud Cloninger, owner of MB Motors forewarned me to expect it before my next scheduled service so it was not a surprise. Since I had replaced the pads on my 93 300E many times, I figures this was a task I could handle myself.
The first thing you should know is that the procedure is very simple but it is nothing like that described in the Service DVD. It’s like the procedure in the service DVD is for the wrong car. So here goes.
| 1. Set the car’s wheels straight ahead. During this whole process you are not going to be able to turn the wheels. | |
| 2. Close all four doors. Barricade them shut. Put caution tap on them. Inform family members that if they open a car door there will be instant death. The reason is that opening a door activates the brake controllers pump. If that happens while you’ve got the pads removed then bad things will happen. Very Bad Things. | |
| 3. Confiscate every key to the car from other family members. Put yours in the pile too. Put the pile as far away from the car as possible. Under lock-and-key if possible. Why? See Step 2. | |
| 4. Unplug the wiring harness from the brake controller. The brake controller is under the hood near the right front corner of the engine compartment. PUll up on the little bracket that my middle finger is under. That bracket locks the connector in place. You should then be able to disconnect the harness from the controller. Stuff a rag between the connector and controller. |  |
| 5. Jack up a wheel and remove the wheel. The brake rotor and caliper should be staring you in the face. |  |
| 6. Disconnect the brake wear sensor. Depending upon year, some cars have a wear sensor on both the left and right front wheels. The One on the left front is different and designed to indicate 50% wear. The sensor on the right front is designed to indicate 25% pad life remaining. My 2006 E350 has one sensor on the right front only. |  |
| 7. Here is what the two sensors look like. The grey one is for the left front. If you are not familiar with Mercedes brakes then I will try to explain. The sensor snaps into a slot on the brake pad and the little rod fits into a hole in the pad material. Eventually the pad wears to the point that the rotor wears through the little rod, breaking the electrical connection and causing the indicator on the instrument panel to come on. Simple and slick. The sensor shown on the left (the lighter-colored one) is designed to plug into the pad on the left front wheel.The hole for the little rod is at the halfway point of the pad’s thickness. The darker colored sensor is designed to plug into a pad on the right front wheel.
When I opened the box, the pads for the left front and right front were the same. The hole in the pad was in the same place. There was no way the lighter-colord sensor would fit. Did I have the wrong pads? The wrong sensor? What gives? It turns out that on my 2006 E350 the left front is not wired for a sensor. Mystery solved. |
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| 8. Losen and remove the lower bolt securing the caliper. It is on the inboard side. |  |
| 9. Loosen and remove the upper bolt securing the caliper. |  |
| 10. With some persuasion you should now be able to lift the caliper off the wheel. Here you can see that I am persuading with a large screwdriver. It should not take much. Just enough to overcome the friction between the caliper’s piston and the pad.
Now that the caliper is off, what are you going to do with it? You don;t want to just leave it hanging my the brake line. Here’s a trick I learned from my aircraft maintenance days: Fasten a couple of zip-ties together and run them through the upper A-arm and the caliper. You now have the caliper secured to the upper A-arm and out of the way. |
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| 11. So now here’s what you are looking at. You should be able to slide the old pads out of the spring rails. If you buy genuine MB pads from the dealership you will find a new set of spring rails in the box. Replace ‘em if you want. I didn’t. |  |
| 12. Plug the wear sensor into the outer pad. |  |
| 13. Peel the backing off the adhesive strip on the inner pad.
Slide the pads onto the brass rails and press them against the rotor. |
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| 14. Now you need to press the piston back into the caliper.
Check the level of brake fluid in the reservoir to make sure that it won’t overflow. If it is in danger of overflowing then remove some. I use a turkey baster for that (but whatever you do, don’t borrow your wife’s baster. Buy your own.) There actually is a specialized tool for pressing the piston back into the caliper. I just use a C-clamp. Gently tighten the C-clamp until it has pushed the piston all the way back into the caliper. |
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| 15. The ends of the pistons have these little spring-clip-plates fastened to the open end. Replacement plates were included in the brake pads from the dealership. It’s really easy to pop them off the piston and then pop them back on (or pop new ones on) after reseating the piston. |  |
| 16. Here you can see the spring-clip-plate snapped onto the open end of the piston. |  |
| 17. Reinstall the caliper and secure the two bolts with a little blue locktite. | |
| 18. Repeat the the other wheel. | |
| 19. Plug the harness back into the brake controller. | |
| 20. Now it’s time for the Christmas Party. “What do I mean”, you ask. After cleaning up a bit and putting everything away, it’s time to start the engine. The instrument cluster will probably light up like a Christmas tree with red warnings about reduced braking effectiveness, etc (I wish I had taken a photo. It was pretty spectacular). Pump the brake pedal a few dozen times. You will also hear the brake controller’s pump running a lot. Turn the ignition off and back on. If the lights are out then you’re done. Other wise pump some more and repeat the process. After a few of these cycles the instrument cluster should look normal when you start the car. | |
You’re done.
